But after the bolt is removed, the crank is still press-fit.
It is not possible to just pull it off:

I was stuck at that point, not knowing what to do next.
The solution which did the work was to insert the bottom bracket cup
removal tool under the crank. Fortunately I had a half-circle wrench,
the "full circle" would not have fit over the crank arm!
The unscrewing cup worked as a crank puller, effectively removing
the left arm from the splined axle.

When the left arm is removed, the work is done: right arm comes off.

I'd say that the claim about "no special tools required for GXP
crank removal" is overstated, because the cups still need a wrench
with a long lever. But it is still better then other designs such
as Shimano Hollowtech and later Sram/Truvativ models, which, in
addition to the cup tool, need a specific left arm extractor or
tightener.